DIGESTION, ETC. OF FAT-SOLUBLE VITAMINS 319 



sis, or regional enteritis. These subjects showed a low or flat vitamin A 

 tolerance curve when vitamin A was given in oil; on the other hand, 

 when PSM solutions of vitamin A were given, a marked increase in the 

 peak levels of vitamin A resulted, 452 with maximum values 400 to 500% 

 higher than those in the control tests. 



Sobel and associates 40 " reported that aqueous solutions of vitamin A 

 are non-toxic. After repeated intravenous injections of the aqueous dis- 

 persion of vitamin A into rabbits, no injury to tissues could be demon- 

 strated by gross examination, by histopathological survey of vital organ 

 sections, or by chemical analysis. However, when corn oil solutions of 

 vitamin A were administered by several routes to vitamin A-deficient rats, 

 Lemley el a/. 453 found that the subcutaneous administration of vitamin A 

 was only 35% as effective as it was by the oral route, while intramuscular 

 injection was only 2% as efficient. 



i'. The Effect of Thyroxine: Reciprocal relationships exist between 

 the metabolism of vitamin A and that of thyroxine. On the one hand, 

 several investigators have reported that large amounts of vitamin A pro- 

 duce an antithyroid action. 4ft4 - 456 On the other hand, the storage of 

 vitamin A in the liver of rats on a diet free from the vitamin was found 

 to be highest in thyroidectomized animals, intermediate in those treated 

 with thyroxine, and least in the control animals. 457 Whether or not this 

 is a reflection of the effect of the thyroid on vitamin A absorption has not 

 been established. The low value of vitamin A in the control rats was 

 interpreted as due to the utilization of vitamin A for growth. 



j'. Miscellaneous Factors Affecting Absorption: Darby, Kaser, and 

 Jones 289 have reported that the ability to absorb vitamin A as well as 

 carotene improved in sprue patients treated with pteroylglutamic acid. 

 When vitamin A was administered to treated patients, an increase in serum 

 vitamin A occurred, as contrasted with a flat cuuve during a relapse after 

 withdrawal of the treatment. 



X-irradiation has little effect on the absorption of vitamin A. Bennett 

 el a/. 458 found an increase in the absorption of vitamin A six hours after 

 feeding vitamin A alcohol to young female rats, two to six days after 



463 J. M. Lemley, R. A. Brown, O. D. Bird, and A. D. Emmett, ./. Nutrition, S3, 53-64 

 (1947). 



454 I. J. Belasco and J. R. Murlin, ./. Nutrition, 20, 577-588 (1940). 



465 D. P. Sadhu and S. Brody, Am. J. Physiol, 149, 400-403 (1947). 



466 E. Sehulze and G. Hundhausen, Arch, exptl. Pathol. Pharmakol. (Naunyn-Schmiede- 

 berg's), 192, 43-52(1939). 



457 C. B. Heimer, H. L. Maslow, and A. E. Sobel, ./. Nutrition, 38, 345-352 (1949). 



458 L. R. Bennett, V. C. Bennett, A. Shaver, and T. Graehus, Proc. So,: Exptl. Biol. 

 Med., 74- 439-443 (1950). 



